1. Field of the Invention
This invention relates to exhaust gas after-treatment systems and more particularly to apparatus, systems and methods for detecting and labeling a filter regeneration event.
2. Description of the Related Art
Environmental concerns have motivated the implementation of emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (EPA) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. Generally, emission requirements vary according to engine type. Emission tests for compression-ignition (diesel) engines typically monitor the release of diesel particulate matter (PM), nitrogen oxides (NOx), and unburned hydrocarbons (UHC). Catalytic converters implemented in an exhaust gas after-treatment system have been used to eliminate many of the pollutants present in exhaust gas. However, to remove diesel particulate matter, typically a diesel particulate filter (DPF) must be installed downstream from a catalytic converter, or in conjunction with a catalytic converter.
A common diesel particulate filter comprises a porous ceramic matrix with parallel passageways through which exhaust gas passes. Particulate matter subsequently accumulates on the surface of the filter, creating a buildup which must eventually be removed to prevent obstruction of the exhaust gas flow. Common forms of particulate matter are ash and soot. Ash, typically a residue of burnt engine oil, is substantially incombustible and builds slowly within the filter. Soot, chiefly composed of carbon, results from incomplete combustion of fuel and generally comprises a large percentage of particulate matter buildup. Various conditions, including, but not limited to, engine operating conditions, mileage, driving style, terrain, etc., affect the rate at which particulate matter accumulates within a diesel particulate filter.
Accumulation of particulate matter typically causes backpressure within the exhaust system. Excessive backpressure on the engine can degrade engine performance. Particulate matter, in general, oxidizes in the presence of NO2 at modest temperatures, or in the presence of oxygen at higher temperatures. If too much particulate matter has accumulated when oxidation begins, the oxidation rate may get high enough to cause an uncontrolled temperature excursion. The resulting heat can destroy the filter and damage surrounding structures. Recovery can be an expensive process.
To prevent potentially hazardous situations, accumulated particulate matter is commonly oxidized and removed in a controlled regeneration process before excessive levels have accumulated. To oxidize the accumulated particulate matter, exhaust temperatures generally must exceed the temperatures typically reached at the filter inlet. Consequently, additional methods to initiate regeneration of a diesel particulate filter may be used. In one method, a reactant, such as diesel fuel, is introduced into an exhaust after-treatment system to initiate oxidation of particulate buildup and to increase the temperature of the filter. A filter regeneration event occurs when substantial amounts of soot are consumed on the particulate filter. Partial or complete regeneration may occur depending on the duration of time the filter is exposed to elevated temperatures and the amount of particulate matter remaining on the filter. Partial regeneration can contribute to irregular distribution of particulate matter across the substrate of a particulate filter.
Controlled regeneration traditionally has been gauged by set intervals, such as distance traveled or time passed. Interval based regeneration, however, has not proven to be effective for several reasons. First, regenerating a particulate filter with little or no particulate buildup lessens the fuel economy of the engine and exposes the particulate filter to unnecessary high temperature cycles. Second, if particulate matter accumulates excessively before the next regeneration, backpressure from blockage of the exhaust flow can negatively affect engine performance. In addition, regeneration with excessive levels of particulates present can potentially cause filter failure or the like. Consequently, particulate filters regenerated on a set interval must be replaced frequently to maintain the integrity of an exhaust gas after-treatment system.
Accurately estimating the amount of particulate matter accumulated in a particulate filter may facilitate determining when to initiate a timely controlled regeneration event. A common method for determining soot accumulation includes using a differential pressure sensor to measure the pressure change of exhaust gas upstream and downstream from a particulate filter. However, a significant factor in causing a backpressure estimate to be incorrect is mal-distribution of particulate matter on the soot filter caused by a partial regeneration of soot.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for detecting and evaluating filter regeneration events. Beneficially, such an apparatus, system, and method would enable a control system to label the filter regenerations events and to provide information about filter regeneration events to other control mechanisms. In addition, the apparatus, system, and method would enable effective and timely regeneration of a diesel particulate filter, increase the fuel economy of a vehicle, extend the life expectancy of a diesel particulate filter, and increase the overall efficiency of an engine.